The present invention relates to an optical fiber sensor.
A catheter is a thin tubular surgical instrument which is inserted into a cavity of a living body to measure the attraction, absorption, and pressure of the liquid in the cavity.
Progressing a step further, an image catheter is an instrument which is used for observing the inside of the cavity, and which is constituted by an image fiber for transmitting an image, a fiber for transmitting illumination light and an outer cover.
FIG. 1 is a schematic diagram of the structure of one example of an image catheter.
The sensor optical fiber 1 is a thin flexible cable or tube to be inserted into the cavity of the body.
The sensor optical fiber 1 has, at its end, a branch mount 2 from which an image fiber 3, an illumination light transmitting optical fiber 4 and a saline solution tube 5 branch.
A direct viewing adaptor 6 is provided at the terminal of the image fiber 3 so that the observer can directly view the inside of the cavity.
A light source 7 is provided at the terminal of the illumination light transmitting optical fiber 4. The light from the light source 7 is transmitted through the light transmitting optical fiber in the sensor optical fiber 1 and projected onto the inside of the cavity to be observed.
A syringe 8 is attached to the terminal of the saline solution tube 5.
The forward end 9 of the sensor optical fiber 1 is inserted into a cavity in the body of a patient or the like. In this example, it is inserted into a blood vessel 10.
The blood vessel 10 is illuminated with light so that an image of the vessel is focused on the end surface of the image fiber 3 by a lens at the forward end 9. The image is transmitted as it is through the image fiber to the direct viewing adaptor 6 and enlarged thereat to be viewed by the observer.
When a blood vessel or the like is observed, the blood existing between the forward end of the catheter and the blood vessel wall becomes a bar to observation and therefore saline solution is injected by a syringe 8 so as to provide a flush of physiological saline solution 11 in the blood vessel 10 to thereby exclude blood therefrom.
FIG. 2 is a cross-section of the conventional sensor optical fiber for use for an image catheter.
The saline solution tube 5 and the image fiber 3 each have a circular cross-section of relatively large diameter and are separated from one another.
Numbers of thin illumination light transmitting optical fibers 4 are disposed in the space between the saline solution tube 5 and the image fiber 3.
The whole of the illumination light transmitting optical fibers 4, the image fiber 3 and the saline solution tube 5 is covered by an outer sheath 12.
In such an arrangement, however, the use efficiency of the available cross-sectional area for illumination light transmission relative to the entire outermost diameter is low, because the illumination light transmitting optical fiber has a circular cross-section. This is because space remains between the illumination light transmitting optical fiber, the saline solution tube, the image fiber, and the outer sheath.
To use the sensor fiber as an image catheter, there is a limitation in that the outer diameter should not exceed 2.3 mm, and this limitation has been a problem in providing an observing device of high efficiency.
In the case where such an image catheter is applied to a dental image fiber device, the configuration is as shown in FIG. 3.
The image fiber 3 and the illumination light transmitting optical fibers 4 are combined at the branch mount 2 and passed through a rigid pipe portion 13. The pipe portion 13 is inserted between a tooth 14 and a tooth-ridge 15 to observe the inside of the ridge 15. In some cases, a hole is bored in a tooth to observe the inside of the tooth.
FIG. 4 is an enlarged cross-section of the rigid tube portion 14
The image fiber 3 and the illumination light transmitting optical fibers 4 each having a circular cross-section are covered with a rigid outer sheath 12.
Since the image fiber 3 and light transmitting optical fibers 4 each having a circular cross-section are used, the volume efficiency is low.
Being inserted into a tooth or tooth-ridge, the rigid pipe portion must have a diameter nor larger than 0.7 mm. For this reason, there is a difficulty in providing the device and therefore this device has not yet been realized.
Endoscopy is widely used in industrial and medical fields. In an endoscope device, a light guide for guiding light and image fibers which are gathered into one flexible tube are generally used.
A light coupling system is required to guide light to the light guide from a light source. In the case where the diameter of the image fiber bundle including the light guide is required to be made especially thin, there are particular difficulties in the structure of the light coupling system.
In an endoscope, in many cases, it is required to apply illumination light to an object to be observed in order to obtain a clear picture image.
Conventionally, a method has been used in which illumination light is externally obtained or in which light from a light source is guided through a light guiding fiber bundle for transmitting illumination light.
In the latter case, the light guiding fiber bundle is provided separately from the image fiber so that it can be freely bent. Accordingly, the terminal of the light guide fiber bundle is directly connected to a light source independently of the image fiber.
FIG. 1A is a cross-section of an image receiving portion of an endoscope for explaining the conventional light coupling system.
An image fiber 42 and a light guiding fiber bundle 43 are separated from each other and are parallelly oriented in a flexible tube 44. An image receiving adaptor 41 is attached to a back end of the flexible tube 44. The light emitted from the back end of the image fiber 42 comes out of the image receiving adaptor 41 through an image receiving lens 45. This picture image is received by a TV camera so as to project the image on a monitor television display or, alternatively, is directly observed.
The light guiding fiber bundle 43 is coupled to a light source 46 through a light source communicating tube 47. There arises no difficulty in separating the image fiber from the light guide in the image receiving portion, because the light guiding fiber bundle is provided separately from the image fiber.
The endoscope is constituted by a forward end image pickup portion for receiving the image of an object, an intermediate long transmission portion and the back end image receiving portion. It is desirable to make the image pickup portion as thin as possible. An image pickup portion having a thin diameter is absolutely required in the case of an endoscope for medical use.
In an endoscope in which the image fiber and the light guiding fiber bundle are contained in the flexible tube in the separated state, the image pickup portion cannot be made sufficiently thin in diameter. The outermost diameter of the image pickup probe becomes 10 to 20 mm.
In many cases for industrial use, a fiber scope having such a thick diameter may be used. In the case for medical use, however, the conventional endoscope is limited to the observation of organs or viscera in which a device of this diameter can be inserted.
It is therefore desired to provide an endoscope having a thinner diameter. With an endoscope having a thinner diameter, the range of organs to be observed will be widened, contributing to an advance in medical treatment. It is not effective to only make thin the diameter of the image fiber. It is necessary to make the light guide for transmitting illumination light thin as well. If the cross-sectional area of the light guide is overly reduced, however, it will become difficult to transmit a sufficient amount of illumination light.